Kerogen extraction from subterranean oil shale resources

ABSTRACT

The present invention is directed to methods for extracting a kerogen-based product from subsurface (oil) shale formations, wherein such methods rely on fracturing and/or rubblizing portions of said formations so as to enhance their fluid permeability, and wherein such methods further rely on chemically modifying the shale-bound kerogen so as to render it mobile. The present invention is also directed at systems for implementing at least some of the foregoing methods. Additionally, the present invention is also directed to methods of fracturing and/or rubblizing subsurface shale formations and to methods of chemically modifying kerogen in situ so as to render it mobile.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present Application is a continuation of U.S. patent applicationSer. No. 12/361,473 filed Jan. 28, 2009, which is a continuation of U.S.patent application Ser. No. 11/675,468, filed Feb. 15, 2007, now U.S.Pat. No. 7,500,517, which claim priority to U.S. Provisional ApplicationNos. 60/774.337, filed Feb. 16, 2006 and 60/846,982, filed Sep. 25,2006. The contents of all of these applications are incorporated hereinby reference in their entirety.

FIELD OF THE INVENTION

This invention relates to methods of extracting organic molecules fromsubterranean shale resources containing an organic kerogen component,particularly wherein such methods involve a step of increasing saidkerogen component's accessibility to a fluid.

BACKGROUND

If proponents of Hubbert peak theory are correct, world oil productionwill soon peak, if it has not done so already. Regardless, world energyconsumption continues to rise at a rate that outpaces new oildiscoveries. As a result, alternative sources of energy must bedeveloped, as well as new technologies for maximizing the production andefficient consumption of oil. See T. Mast, Over a Barrel: A Simple Guideto the Oil Shortage, Greenleaf Book Group, Austin, Tex., 2005.

A particularly attractive alternative source of energy is oil shale, theattractiveness stemming primarily from the fact that oil can be“extracted” from the shale and subsequently refined in a manner muchlike that of crude oil. Technologies involving the extraction, however,must be further developed before oil shale becomes a commercially-viablesource of energy. See J. T. Bartis et al. Oil Shale Development in theUnited States: Prospects and Policy Issues, RAND Corporation, Arlington,Va., 2005.

The largest known deposits of oil shale are found in the Green RiverFormation, which covers portions of Colorado, Utah, and Wyoming.Estimates on the amount of recoverable oil from the Green RiverFormation deposits are as high as 1.1 trillion barrels of oil—almostfour times the proven oil reserves of Saudi Arabia. At current U.S.consumption levels (˜20 million barrels per day), these shale depositscould sustain the U.S. for another 140 years (Bartis et al.). At thevery least, such shale resources could moderate the price of oil andreduce U.S. dependence on foreign oil.

Oil shale typically consists of an inorganic component (primarilycarbonaceous material, i.e., a carbonate) and an organic component(kerogen). Thermal treatment can be employed to break (i.e., “crack”)the kerogen into smaller hydrocarbon chains or fragments, which are gasor liquids under retort conditions, and facilitate separation from theinorganic material. This thermal treatment of the kerogen is also knownas “thermal upgrading” or “retorting,” and can be done at either thesurface or in situ, where in the latter case, the fluids so formed aresubsequently transported to the surface.

In some applications of surface retorting, the oil shale is first minedor excavated, and once at the surface, the oil shale is crushed and thenheated (retorted) to complete the process of transforming the oil shaleto a crude oil—sometimes referred to as “shale oil.” See, e.g., Shumanet al., U.S. Pat. No. 3,489,672. The crude oil is then shipped off to arefinery where it typically requires additional processing steps (beyondthat of traditional crude oil) prior to making finished products such asgasoline, lubricant, etc. Note that various chemical upgradingtreatments can also be performed on the shale prior to the retorting.See, e.g., So et al., U.S. patent application Ser. No. 5,091,076.

A method for in situ retorting of carbonaceous deposits such as oilshale has been described in Kvapil et al., U.S. patent application Ser.No. 4,162,808. In this method, shale is retorted in a series ofrubblized in situ retorts using combustion (in air) of carbonaceousmaterial as a source of heat.

The Shell Oil Company has been developing new methods that useelectrical heating for the in situ upgrading of subsurface hydrocarbons,primarily in subsurface formations located approximately 200 miles (320km) west of Denver, Colo. See, e.g., Vinegar et al., U.S. Pat. No.7,121,342; and Berchenko et al., U.S. Pat. No. 6,991,032. In suchmethods, a heating element is lowered into a well and allowed to heatthe kerogen over a period of approximately four years, slowly converting(upgrading) it into oils and gases, which are then pumped to thesurface. To obtain even heating, 15 to 25 heating holes could be drilledper acre. Additionally, a ground-freezing technology to establish anunderground barrier around the perimeter of the extraction zone is alsoenvisioned to prevent groundwater from entering and the retortingproducts from leaving. While the establishment of “freeze walls” is anaccepted practice in civil engineering, its application to oil shalerecovery still has unknown environmental impacts. Additionally, theShell approach is recognized as an energy intensive process and requiresa long timeframe to establish production from the oil shale.

In view of the aforementioned limitations of the above methods, simplerand more cost-effective methods of extracting the kerogen from the shalewould be extremely useful.

BRIEF DESCRIPTION OF THE INVENTION

The present invention is generally directed to methods of extracting akerogen-based product from subsurface (oil) shale formations, whereinsuch methods rely on fracturing and/or rubblizing portions of saidformations so as to enhance their fluid permeability (e.g., providing afluid greater accessibility to the shale-bound kerogen), and whereinsuch methods further rely on chemically modifying the shale-boundkerogen so as to render it mobile. The present invention is alsodirected to systems for implementing some such methods. Additionally, tothe extent that they are themselves novel, the present invention is alsodirected to methods of fracturing and/or rubblizing subsurface shaleformations and to methods of chemically modifying kerogen in situ so asto render it mobile.

In some embodiments, the present invention is directed to methods forextracting a kerogen-based product from a subsurface shale formationcomprising subsurface shale, the methods comprising the steps of: (a)increasing accessibility of kerogen in subsurface shale to a fluid,wherein the subsurface shale comprises an inorganic component inaddition to the kerogen; (b) contacting the kerogen in the subsurfaceshale with an extraction fluid to create a mobile kerogen-based product;and (c) transporting the mobile kerogen-based product out of thesubsurface shale formation to yield an extracted kerogen-based product.

In some such above-described method embodiments, the step of increasingaccessibility comprises the sub-steps of: (a) drilling a cased injectionwell into the subsurface shale formation comprising the subsurfaceshale; (b) pressurizing and subsequently sealing the injection well witha dense phase fluid to provide a pressurized well; and (c) rapidlyde-pressurizing the pressurized well to reach a steady state reducedpressure. In some such embodiments, the sub-steps of pressurizing andde-pressurizing are repeated.

In some embodiments, the present invention is directed to methods forfracturing and/or rubblizing subsurface shale formations comprisingsubsurface oil shale, wherein the subsurface shale comprises kerogen andan inorganic component, and wherein said fracturing and/or rubblizingenhances the fluid permeability of the subsurface shale, the methodscomprising the steps of: (a) drilling a cased injection well into thesubsurface shale formation comprising the subsurface shale; (b)delivering a slurry to the injection well, the slurry comprising liquidCO₂ and solid CO₂, and sealing the injection well so as to establish asealed well; (c) pressurizing the sealed well by permitting the liquidCO₂ and solid CO₂ inside the sealed well to form supercritical CO₂,thereby forming a pressurized well; and (d) depressurizing thepressurized well to reach a steady state reduced pressure, whereby anassociated adiabatic expansion of the CO₂ cools the subsurface shaleformation and causes thermal and mechanical stresses within theformation which in turn lead to fracturing of said formation. In somesuch embodiments, the steps of pressurizing and de-pressurizing arerepeated until an equilibrium pressure is reached.

In some embodiments, the present invention is directed to methods ofchemically modifying the kerogen within oil shale so as to render itmobile and subsequently extractable. Such chemical modificationgenerally involves breaking of chemical bonds within the kerogen (i.e.,cracking) and/or between the kerogen and the inorganic shale component.Such chemical modification can also involve a delamination of thekerogen from the inorganic shale component. The ability to chemicallymodify the kerogen in this manner is largely predicated on the abilityto increase the kerogen's accessibility to a fluid that can effect sucha chemical modification.

In some embodiments, the present invention is directed to methodscomprising the steps of: (a) analyzing a subsurface kerogen-bearingshale formation so as to derive information regarding the kerogencontained therein; (b) increasing accessibility of said kerogen in thesubsurface shale to a fluid, wherein the subsurface shale comprises aninorganic component in addition to the kerogen; (c) monitoring theincreased accessibility provided in step (b); (d) contacting the kerogenin the subsurface shale with a reactive fluid to create a mobilekerogen-based product, wherein said reactive fluid is selected in viewof the information derived in step (a); and (e) transporting the mobilekerogen-based product out of the subsurface shale formation to yield anextracted kerogen-based product. Optionally, such methods can furthercomprise a step of processing the extracted kerogen-based product.

In some embodiments, the present invention is directed to systemscomprising: (a) a means for analyzing a subsurface kerogen-bearing shaleformation so as to derive information regarding the kerogen containedtherein; (b) a means for increasing accessibility of said kerogen in thesubsurface shale to a fluid, wherein the subsurface shale comprises aninorganic component in addition to the kerogen; (c) a means formonitoring the increased accessibility provided by means (b); (d) ameans of contacting the kerogen in the subsurface shale with a reactivefluid to create a mobile kerogen-based product, wherein said reactivefluid is selected in view of the information derived by means (a); and(e) a means for transporting the mobile kerogen-based product out of thesubsurface shale formation to yield an extracted kerogen-based product.Optionally, such a system can further comprise a means for processingthe extracted kerogen-based product.

Providing extension to other types of oil- and/or gas-bearingformations, in some embodiments, the present invention is directed tomethods for extracting a hydrocarbon-based product from alow-permeability hydrocarbon-bearing subsurface formation, the methodscomprising the steps of: (a) increasing permeability in a region of thesubsurface formation to a fluid so as to establish a region of enhancedpermeability; (b) contacting hydrocarbonaceous material in the region ofenhanced permeability with a reactive fluid to create a mobilehydrocarbon-based product; and (c) transporting the mobilehydrocarbon-based product out of the subsurface formation to yield anextracted hydrocarbon-based product. In some such embodiments, the stepof increasing permeability comprises the sub-steps of: (aa) drilling acased injection well into the subsurface formation; (ab) pressurizingthe injection well with a dense phase fluid to provide a pressurizedwell; and (ac) rapidly de-pressurizing the pressurized well to reach asteady state reduced pressure. In some such latter embodiments, thesub-steps of pressurizing and de-pressurizing are repeated until anequilibrium pressure is reached.

The foregoing has outlined rather broadly the features of the presentinvention in order that the detailed description of the invention thatfollows may be better understood. Additional features and advantages ofthe invention will be described hereinafter which form the subject ofthe claims of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 depicts, in stepwise fashion, a general method of chemicallymodifying subsurface shale-bound kerogen so as to render it mobile andtherefore extractable;

FIG. 2 depicts, in stepwise fashion, a method of increasing fluidaccessibility to the kerogen, in accordance with some embodiments of thepresent invention;

FIG. 3 depicts, in stepwise fashion, integrated processing methods ofextracting a petroleum-based product from subsurface oil shale, inaccordance with some embodiments of the present invention.

FIG. 4 is a flow diagram illustrating a system for implementing someintegrated processing method embodiments of the present invention; and

FIG. 5 is a schematic showing how a subsurface shale formation can befractured, in accordance with some system and/or method embodiments ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION 1. Introduction

The present invention is directed to methods of extracting akerogen-based product from subsurface (oil) shale formations, whereinsuch methods rely on fracturing and/or rubblizing portions of saidformations so as to enhance their fluid permeability, and wherein suchmethods further rely on chemically modifying the shale-bound kerogen soas to render it mobile. The present invention is also directed tosystems for implementing some such methods.

2. Definitions

“Shale,” as defined herein, generally refers to “oil shale” and is ageneral term applied to a group of rocks rich enough in organic material(called kerogen) to yield petroleum upon pyrolysis and distillation.Such shale is generally subsurface and comprises an inorganic (usuallycarbonate) component in addition to the kerogen component.

“Kerogen,” as defined herein and as mentioned above, is an organiccomponent of shale. On a molecular level, kerogen comprises very highmolecular weight molecules that are generally insoluble by virtue oftheir high molecular weight and likely bonding to the inorganiccomponent of the shale. The portion of kerogen that is soluble is knownas “bitumen;” bitumen typically being the heaviest component of crudeoil. In fact, in a geologic sense, kerogen is a precursor to crude oil.Kerogen is typically identified as being one of five types: Type I, TypeII, Type II-sulfur, Type III, or Type IV, based on its C:H:O ratio andsulfur content, the various types generally being derived from differentsources of ancient biological matter.

“Kerogen-based,” is a term used herein to denote a molecular product orintermediate derived from kerogen, such derivation requiring a chemicalmodification of the kerogen, and the term being exclusive of derivationscarried out over geologic timescales.

A “subsurface shale formation,” as defined herein, is an undergroundgeological formation comprising (oil) shale.

A “low-permeability hydrocarbon-bearing formation,” as defined herein,refers to formations having a permeability of less than about 10millidarcies, wherein said formations comprise hydrocarbonaceousmaterial. Examples of such formations include, but are not limited to,diatomite, coal, tight shales, tight sandstones, tight carbonates, andthe like.

A “dense phase fluid,” as defined herein, is a non-gaseous fluid. Suchdense phase fluids include liquids and supercritical fluids (SCFs).

A “supercritical fluid,” as defined herein and as mentioned above, isany substance at a temperature and pressure above its thermodynamiccritical point. Supercritical fluids can be regarded as “hybridsolvents” with properties between those of gases and liquids, i.e., asolvent with a low viscosity, high diffusion rates and no surfacetension. The most common supercritical fluids are supercritical carbondioxide (CO₂) and supercritical water.

The term “mechanical stress,” as used herein, refers to structuralstresses within the shale formation that result from pressure variationswithin the formation. Such stress can lead to fracturing and/orrubblization of the shale formation.

The term “thermal stress,” as used herein, refers to structural stresseswithin the shale formation that result from thermal variations. Suchthermal stresses can induce internal mechanical stresses as a result ofdifferences in thermal coefficients of expansion among the variouscomponents of the shale formation. Like mechanical stress mentionedabove, thermal stress can also lead to fracturing and/or rubblization ofthe shale formation.

The term “fracturing,” as used herein, refers to the structuraldegradation of a subsurface shale formation as a result of appliedthermal and/or mechanical stress. Such structural degradation generallyenhances the permeability of the shale to fluids and increases theaccessibility of the kerogen component to such fluids. The term“rubblization,” as used herein, is a more extensive fracturing processyielding fracture planes in multiple directions that generateshale-derived “rubble.”

The term “cracking,” as mentioned in the background section and as usedherein, refers to the breaking of carbon-carbon bonds in the kerogen soas to yield species of lower molecular weight. “Retorting,” providesthermal cracking of the kerogen. “Upgrading,” provides cracking of thekerogen, but can involve a thermal or chemical upgrading agent.Accordingly, the term “thermal upgrading” is synonymous with the term“retorting.”

The term “in situ,” as used herein with regard to cracking or upgradingof kerogen, refers to such cracking or upgrading being carried out inthe kerogen's native environment. In contrast to the in situ Shellmethod described in the background section, methods of the presentinvention are not truly done in situ because some fracturing of theshale formation must be done first, thereby altering the kerogen'senvironment from its native state.

The term “commercial petroleum-based products,” as used herein, refersto commercial products that include, but are not limited to, gasoline,aviation fuel, diesel, lubricants, petrochemicals, and the like. Suchproducts could also include common chemical intermediates and/orblending feedstocks.

3. Method Overview

Referring to FIG. 1, in some embodiments, the present invention isgenerally directed to methods for extracting a kerogen-based productfrom a subsurface shale formation comprising subsurface shale, themethods comprising the steps of: (Step 101) increasing accessibility ofkerogen in subsurface shale to a fluid (e.g., increasing thepermeability of the shale), wherein the subsurface shale comprises aninorganic component in addition to the kerogen; (Step 102) contactingthe kerogen in the subsurface shale with an extraction fluid (or fluids)to create a mobile kerogen-based product; and (Step 103) transportingthe mobile kerogen-based product out of the subsurface shale formationto yield an extracted kerogen-based product.

The above-mentioned step of increasing the accessibility of thesubsurface shale to a fluid (Step 101) may include a variety oftechniques and/or technologies such as, but not limited to, explosives,hydraulic fracturing, propellants, and the like. Generally, any methodof fracturing and/or rubblizing regions of the shale formation, so as torender said shale more permeable to fluids, is suitable. Such fracturingand/or rubblizing can also involve chemicals reactive to, e.g., at leastpart of the inorganic shale component.

The step of contacting the kerogen with an extraction fluid (Step 102)generally involves an in situ chemical modification of the kerogen(e.g., cracking) and/or surrounding shale so as to render the modifiedkerogen component mobile (vide infra). Such chemical modificationgenerally involves the making and/or breaking of chemical bonds.

The step of transporting the mobile kerogen-based product out of thesubsurface shale formation (Step 103) is not particularly limited, butcan generally be described as a means of flowing the mobilekerogen-based product out of the subsurface formation, where such ameans can be active (e.g., pumping) and/or passive.

In some embodiments, the above-described method may involve one or moreadditional steps which serve to sample and subsequently analyze theshale prior to performing Step 101. Such sampling and analysis can havea direct bearing on the techniques employed in the subsequent steps.

In some embodiments, analysis and/or monitoring of the fracturing and/orrubblizing of the subsurface shale formation can be carried out duringor after Step 101. Such analysis and/or monitoring can be performedusing techniques known in the art for accomplishing such tasks.

In some embodiments, the extracted kerogen-based product is upgraded(thermally and/or chemically) at the surface. Such surface upgrading canbe intermediate to subsequent refining.

4. Increasing Fluid Accessibility to the Kerogen

Simultaneously referring to the above-described method and FIG. 2, insome embodiments, the step of increasing accessibility (Step 101)comprises the sub-steps of: (Sub-step 201) drilling a cased injectionwell into the subsurface shale formation comprising the subsurfaceshale; (Sub-step 202) pressurizing and subsequently sealing theinjection well with a dense phase fluid to provide a pressurized well;and (Sub-step 203) rapidly de-pressurizing the pressurized well to reacha steady state reduced pressure. In some such embodiments, the sub-stepsof pressurizing and de-pressurizing are repeated until an equilibriumpressure is reached.

The dense phase fluid can be any such fluid that suitably provides forincreased accessibility of the kerogen to a fluid—typically due tofracturing and/or rubblizing of the shale in which the kerogen resides.In some embodiments, the dense phase fluid comprises a componentselected from the group consisting of carbon dioxide (CO₂), nitrogen(N₂), liquid natural gas (LNG), ammonia (NH₃), carbon monoxide (CO),argon (Ar), liquefied petroleum gas (LPG), hydrogen (H₂), hydrogensulfide (H₂S), air, C₁ to C₂₀ hydrocarbons (including, but not limitedto, ethane, propane, butane, and combinations thereof), and the like.

In some embodiments, the pressure in the pressurized well exceeds thefracture pressure of the subsurface shale formation. Such formationfracture pressure could be ascertained beforehand, for example—therebyhelping to direct the choice of variable parameters used in this step.

In some embodiments, the dense phase fluid is absorbed by the kerogenand the kerogen subsequently swells, and wherein the swollen kerogenexpands the subsurface shale formation and creates mechanical stressesleading to subsequent fracturing and/or rubblization of said formation.In some such embodiments, the mechanical stresses created during thepressurizing and depressurizing sub-steps enhance fracturing and/orrubblization of the subsurface shale formation.

In some embodiments, the pressurizing and depressurizing sub-stepscreate thermal and/or mechanical stresses in the subsurface shaleformation. In some such embodiments, the kerogen at least partiallydelaminates from the inorganic component of the shale as a result of thethermal stresses.

In some embodiments, explosives are added to the dense phase fluid toenhance rubblization and fracturing of the formation. Examples of suchexplosives include, but are not limited to, strongly oxidizing species,nitro-containing species (e.g., trinitrotoluene, nitroglycerine),thermite mixtures, and the like. The dense phase fluids to which suchexplosives can be added include, but are not limited to, carbon dioxide(CO₂), nitrogen (N₂), liquid natural gas (LNG), ammonia (NH₃), carbonmonoxide (CO), argon (Ar), liquefied petroleum gas (LPG), hydrogen (H₂),hydrogen sulfide (H₂S), air, C₁ to C₂₀ hydrocarbons (including, but notlimited to, ethane, propane, butane, and combinations thereof), and thelike.

5. Creating a Mobile Kerogen-Based Product

In some embodiments, the step of contacting the kerogen in thesubsurface shale with a reactive fluid to create a mobile kerogen-basedproduct involves a chemical modification of the kerogen. In some suchembodiments, the chemical modification involves at least some crackingof the kerogen, generating smaller kerogen-derived molecules that arecorrespondingly more mobile.

In general, the reactive fluid is any fluid (including mixtures) thatcan, either by itself or with an agent dissolved therein, chemicallymodify the kerogen so as to render it mobile and therefore extractable.In some embodiments, the reactive fluid comprises a reactive componentselected from the group consisting of organic acids (e.g., formic acid),inorganic acids (e.g., hydrochloric), peroxides (e.g., H₂O₂), freeradical producing chemicals (e.g., F₂), Lewis acids (e.g., AlCl₃), humicdepolymerization agents (e.g., amines), olefin metathesis catalysts(e.g., W), reactive gases (e.g., Cl₂), enzymes (e.g., lipase), microbes(e.g., pseudomas), plasmas (e.g., He), catalysts (e.g., pyrite, in situtransition metals), and combinations thereof. Typically, such reactivecomponents are dispersed, dissolved, or otherwise incorporated into adense phase fluid. As above, suitable such dense phase fluids include,but are not limited to, carbon dioxide (CO₂), nitrogen (N₂), liquidnatural gas (LNG), ammonia (NH₃), carbon monoxide (CO), argon (Ar),liquefied petroleum gas (LPG), hydrogen (H₂), hydrogen sulfide (H₂S),air, C₁ to C₂₀ hydrocarbons (including, but not limited to, ethane,propane, butane, and combinations thereof), and the like.

In some embodiments, depending on the conditions and reactive fluidsemployed and on the kerogen bonds that are broken, it is possible togenerate a mobile kerogen-based product that is tailored so as tominimize recovery of heavy metals and/or other undesirable materials, orto increase recovery by reducing char and/or other carbon residues.Accordingly, it is possible to generate a mobile kerogen-based productthat requires little or no additional refining.

6. Producing the Mobile Kerogen-Based Product

In some embodiments, the mobile kerogen-based product is extracted fromthe subsurface formation using an extraction fluid. Suitable extractionfluids, like the dense phase fluids, include, but are not limited to,carbon dioxide (CO₂), nitrogen (N₂), liquid natural gas (LNG), ammonia(NH₃), carbon monoxide (CO), argon (Ar), liquefied petroleum gas (LPG),hydrogen (H₂), hydrogen sulfide (H₂S), air, C₁ to C₂₀ hydrocarbons(including, but not limited to, ethane, propane, butane, andcombinations thereof), and the like. In some embodiments, the extractionfluid is substantially indistinguishable from the reactive fluid (seeabove).

In some embodiments, it is contemplated that the mobile kerogen-basedproduct comprises a slurry of kerogen particulates in the extractionfluid. Accordingly, such mobile kerogen-based product need not bedissolved in such a fluid.

In some embodiments, pumping is used to transport the mobilekerogen-based product out of the subsurface shale formation, whereinsuch pumping can be performed using techniques known to those of skillin the art. Conventional oil field practices (both flowing gas andpumping fluids, e.g., rod pumps, electrical submersible pumps,progressive cavity pumps, etc.) can be modified to provide reliabilityin a given producing environment. For example, modifications may requirechanges in metallurgy, pressure limitations, elastomeric compositions,temperature rating, and the like.

Production could use any standard producing process such as, but notlimited to, Huff-n-Puff (i.e., a single well is used as both theproducer and injector), water flooding, steam flooding, polymerflooding, solvent extraction flooding, thermal processes, diluentaddition, steam assisted gravity drainage (SAGD), and the like.

7. Upgrading the Extracted Kerogen-Based Product

In some embodiments, the extracted kerogen-based product is upgraded toyield one or more commercial petroleum-based products. Various surfacetechniques common in the industry (e.g., catalytic cracking,hydroprocessing, thermal cracking, denitrofication, desulfurization) maybe employed to obtain a desired commercial product from the extractedkerogen-based product. Such surface upgrading is largely dependent onthe nature of the extracted kerogen-based product relative to thecommercial product that is desired.

8. Integrated Production Method

Referring to FIG. 3, in some embodiments, the present invention isdirected to integrated production methods comprising the steps of: (Step301) analyzing a subsurface kerogen-bearing shale formation so as toderive information regarding the kerogen contained therein; (Step 302)increasing accessibility of said kerogen in the subsurface shale to afluid, wherein the subsurface shale comprises an inorganic component inaddition to the kerogen; (Step 303) monitoring the increasedaccessibility provided in Step 302; (Step 304) contacting the kerogen inthe subsurface shale with a reactive fluid to create a mobilekerogen-based product, wherein said reactive fluid is selected in viewof the information derived in Step 301; (Step 305) transporting themobile kerogen-based product out of the subsurface shale formation toyield an extracted kerogen-based product; and (Step 306) optionallyprocessing the extracted kerogen-based product.

Generally, such above-described integrated production methods areconsistent (in terms of their common steps) with the aforementionedmethods of extracting a kerogen-based product from a subsurface shaleformation. See above for more detail on the various steps shared by suchmethods.

9. Integrated Production System

Referring to FIG. 4, in some embodiments, the present invention isdirected to integrated production systems comprising: (Means 401) ameans for analyzing a subsurface kerogen-bearing shale formation so asto derive information regarding the kerogen contained therein; (Means402) a means for increasing accessibility of said kerogen in thesubsurface shale to a fluid, wherein the subsurface shale comprises aninorganic component in addition to the kerogen; (Means 403) a means formonitoring the increased accessibility provided by Means 402; (Means404) a means (mobilizing means) of contacting the kerogen in thesubsurface shale with a reactive fluid to create a mobile kerogen-basedproduct, wherein said reactive fluid is selected in view of theinformation derived by Means 401; (Means 405) a means (extraction means)for transporting the mobile kerogen-based product out of the subsurfaceshale formation to yield an extracted kerogen-based product; and (Means406) a means for optionally processing the extracted kerogen-basedproduct.

Like the integrated process methods, such above-described systemembodiments are generally consistent with the aforementioned methods ofextracting a kerogen-based product from a subsurface shale formation.Notwithstanding such general consistencies, exemplary such means areprovided below.

Still referring to FIG. 4, Means 401 can include subsurface analyzingtechnologies such as, but not limited to, well logging, core samplingand analysis (incl. kerogen chemical analysis), and the like. Means 402can include a means or subsystem for increasing fluid accessibility tothe kerogen, wherein such a subsystem implements the sub-steps outlinedin FIG. 2. Means 403 can include subsurface monitoring technologies suchas, but not limited to, tilt-meters, microseismic techniques (involvinggeophones), and the like. See, e.g., Phillips. W. S., et al., “Reservoirmapping using microearthquakes: Austin Chalk, Giddings field, TX and 76field. Clinton Co., Ky.,” SPE 36651, Annual Technical Conference andExhibition, Denver, Colo., Oct. 6-9, 1996. Means 404 typically comprisesa subsystem for pumping a dense phase fluid into a fractured subsurfaceshale resource, wherein the fluid may further comprise agents operablefor chemically modifying the kerogen so as to render it mobile. Means405 typically comprises a subsystem for extracting a mobilekerogen-based product from the subsurface, wherein such a subsystem maycomprise an extraction fluid (see above) and a pumping technology.Finally, Means 406 can involve any processing sub-system whichoptionally processes the extracted kerogen-based product to yield adesired product or intermediate. Exemplary such Means 406 include, butare not limited to, conventional retorting, pipeline transport,conventional separation techniques, and the like.

10. Variations

A variation (i.e., alternate embodiment) on the above-described processis the application of some or part of such above-described methods toalternative sources, i.e., low-permeability hydrocarbon-bearing (e.g.,oil and gas) formations, in situ coal, in situ heavy oil, in situ oilsands, and the like. General applicability of at least some of theabove-described invention embodiments to any hydrocarbon-bearingformation exists. Surface processing applications may include upgradingof oil shale, coal, heavy oil, oil sands, and other conventional oilswith asphaltenes, sulfur, nitrogen, etc.

11. Examples

The following examples are provided to demonstrate particularembodiments of the present invention. It should be appreciated by thoseof skill in the art that the methods disclosed in the examples whichfollow merely represent exemplary embodiments of the present invention.However, those of skill in the art should, in light of the presentdisclosure, appreciate that many changes can be made in the specificembodiments described and still obtain a like or similar result withoutdeparting from the spirit and scope of the present invention.

Example 1

This Example serves to illustrate how shale in a subsurface formationcan be sampled and analyzed prior to fracturing and/or rubblizing, inaccordance with some embodiments of the present invention.

Whole or conventional cores can be obtained using standard core samplingtechniques known in the art and using bits such as Baker Hughes INTEQcoring bits. Sidewall and sidewall rotary cores can also be obtained,but these are typically smaller and generally of lower quality. Onceobtained, the core samples can be subjected to a variety of analysesincluding, but not limited to, core gamma analysis, density,circumferential imaging and computed tomography (CT) scanning, fractureanalysis, permeability, porosity, hydrocarbon recovery when exposed tothe reactive fluid, electrical measurements, thermal conductivitymeasurements, rock mechanics, X-ray diffraction (XRD), nuclear magneticresonance (NMR), total organic carbon (TOC), fluorescence and/orinfrared spectroscopy, etc.

Information obtained from such core analysis can serve as a guide inselecting the appropriate reagents (e.g., fluids) and conditions used inimplementing the methods and systems of the present invention.

In addition to, or instead of, water sampling (vide infra), well-loggingcan also be carried out to compliment the information obtained via coresampling. Such techniques can yield information about how the formationvaries with depth.

Example 2

This Example serves to illustrate fracturing and/or rubblizing of shalein a subsurface shale formation so as to increase fluid accessibility tothe kerogen contained therein, in accordance with some embodiments ofthe present invention, and particularly within the context of theexemplary system embodiment depicted in FIG. 5.

Referring to FIG. 5, integrated system 500 comprises establishing aninjection well 501 that extends into the subsurface through the (e.g.,Uinta) formation 502 and the (e.g., Green River) formation 503, whereinthe latter is subdivided into three zones (503 a, 503 b, and 503 c).Fluids are injected into the formation via injection well 501 andprovide a fractured formation 503 b having increased fluid accessibilityto the kerogen contained therein. Such fluid access further provides forcontacting the kerogen with a reactive fluid and extraction fluid so asto extract the mobile kerogen-based product out of the formation via oneor more producing wells 505 to yield an extracted kerogen-based product.Note that water monitoring can be carried out, for example, viagroundwater monitoring wells 506 to verify that no groundwatercontamination has occurred as a result of fracturing into existingaquifers. One extracted, the extracted kerogen-based product can betransported via pipe to separator/treatment and production tanks.

Example 3

This Example serves to illustrate how the fracturing and/or rubblizingof shale in a subsurface shale formation can be monitored, in accordancewith some embodiments of the present invention.

In lieu of, or in addition to, the groundwater monitoring well(s)described in Example 2, tiltmeters can be installed in a patternedarrangement on the surface of the shale formation. The tiltmeterinstallations would be in 8.5 inch holes, 25 feet deep, and lined withPVC pipe and perhaps a little cement on the bottom. They would be cappedand have a solar panel for data collection. Geophones can also beinstalled either at the surface or sub-surface to gather micro-seismicinformation to help track fracture growth.

Example 4

This Example serves to illustrate the process of contacting theshale-bound kerogen with a reactive fluid, and how the kerogen can bechemically modified in situ, in accordance with some embodiments of thepresent invention.

Such an exemplary process would involve the injection of a dense phasefluid such as carbon dioxide in a liquid phase and a reactive co-solventsuch as formic acid in a concentration that would allow for a singlephase system at the formation temperature and pressure. Optimalperformance would be achieved with pressure and temperatures above thecritical point of the dense phase fluid, i.e., 1070 pisg and 31° C. forCO₂. The supercritical fluid (SCF) will have optimal penetration intothe low permeable formation due to the supercritical fluids lowdiffusivity and undefined (zero) surface tension. The SCF willsolubilize the co-solvent/additive (e.g., formic acid) to allow contactwith both the inorganic and organic component of the oil shale. Thiscontact will allow for a chemical reaction to occur with the organic andcarbonate inorganic material in the oil shale to convert the materialsto gas and/or small molecular size creating increased surface area andsmaller molecular weight kerogen.

Example 5

This Example serves to illustrate how the mobile kerogen-based productcan be extracted from the subsurface formation, in accordance with someembodiments of the present invention.

Once the kerogen is converted to a mobile kerogen-based product, anextraction fluid can be used to transport it to the surface. Typically,the extraction fluid is substantially similar in composition to that ofthe reactive fluid, albeit typically somewhat depleted in the reactiveagent. Referring again to FIG. 5, and utilizing an extraction fluidresembling the reactive fluid described in Example 4, said extractionfluid is pumped into the formation via injection well(s) 501, contactsthe mobile kerogen-based product in the fractured formation 504, and ispumped to the surface via production well(s) 505, transporting themobile kerogen-based product along with it, thereby providing for anextracted kerogen-based product.

Example 6

This Example serves to illustrate post-extraction processes that can beperformed on the extracted kerogen-based product, in accordance withsome embodiments of the present invention.

If the extracted kerogen-based product comprises a substantial portionof high molecular weight species that render the product highly viscous,surface upgrading can be used to thermally-crack or “visbreak” theproduct to yield a lower-viscosity, more-easily-transportable product.Doing this within the immediate proximity of the extraction site canmake good economic sense in that the lower viscosity product could thenbe more easily transported across long distances via pipeline.

12. Summary

The present invention is directed to methods for extracting akerogen-based product from subsurface (oil) shale formations, whereinsuch methods rely on fracturing and/or rubblizing portions of saidformations so as to enhance their fluid permeability, and wherein suchmethods further rely on chemically modifying the shale-bound kerogen soas to render it mobile. The present invention is also directed atsystems for implementing such methods. The present invention is alsodirected to methods of fracturing and/or rubblizing subsurface shaleformations and to methods of chemically modifying kerogen in situ so asto render it mobile.

13. Conclusion

All patents and publications referenced herein are hereby incorporatedby reference to the extent not inconsistent herewith. It will beunderstood that certain of the above-described structures, functions,and operations of the above-described embodiments are not necessary topractice the present invention and are included in the descriptionsimply for completeness of an exemplary embodiment or embodiments. Inaddition, it will be understood that specific structures, functions, andoperations set forth in the above-described referenced patents andpublications can be practiced in conjunction with the present invention,but they are not essential to its practice. It is therefore to beunderstood that the invention may be practiced otherwise than asspecifically described without actually departing from the spirit andscope of the present invention as defined by the appended claims.

1. A method for extracting a kerogen-based product from a subsurfaceshale formation comprising subsurface shale, wherein the subsurfaceshale comprises an inorganic component in addition to the kerogen, themethod comprising the steps of: a) increasing accessibility of kerogenin subsurface shale to a fluid by (i) drilling a cased injection wellinto the subsurface shale formation comprising the subsurface shale;(ii) pressurizing the injection well with a dense phase fluid to providea pressurized well; and (iii) rapidly de-pressurizing the pressurizedwell to reach a steady state reduced pressure, wherein the kerogenabsorbs a portion of the dense phase fluid; b) contacting the kerogen inthe subsurface shale with a reactive fluid to create a mobilekerogen-based product; and c) transporting the mobile kerogen-basedproduct out of the subsurface shale formation to yield an extractedkerogen-based product.
 2. The method of claim 1, wherein the sub-stepsof pressurizing and de-pressurizing are repeated.
 3. The method of claim1, wherein the dense phase fluid comprises a component selected from thegroup consisting of carbon dioxide (CO₂), nitrogen (N₂), liquid naturalgas (LNG), ammonia (NH₃), carbon monoxide (CO), argon (Ar), liquefiedpetroleum gas (LPG), hydrogen (H₂), hydrogen sulfide (H₂S), air, C₁ toC₂₀ hydrocarbons, and combinations thereof.
 4. The method of claim 1,wherein the pressure in the pressurized well exceeds the fracturepressure of the subsurface shale formation.
 5. The method of claim 1,wherein the dense phase fluid is absorbed by the kerogen and the kerogensubsequently swells, and wherein the swollen kerogen expands thesubsurface shale formation and creates mechanical stresses leading tosubsequent fracturing and rubblization of said formation.
 6. The methodof claim 1, wherein the mechanical stresses created during thepressurizing and depressurizing sub-steps enhance fracturing of thesubsurface shale formation.
 7. The method of claim 1, wherein thepressurizing and depressurizing sub-steps create thermal stresses in thesubsurface shale formation.
 8. The method of claim 7, wherein kerogen atleast partially delaminates from the inorganic component of the shale asa result of the thermal stresses.
 9. The method of claim 1, whereinexplosives are added to the dense phase fluid to enhance rubblizationand fracturing of the formation.
 10. The method of claim 1, wherein thestep of contacting the kerogen in the subsurface shale with a reactivefluid to create a mobile kerogen-based product involves a chemicalmodification of the kerogen.
 11. The method of claim 10, wherein thechemical modification involves at least some cracking of the kerogen.12. The method of claim 1, wherein the reactive fluid comprises a firstcomponent selected from the group consisting of carbon dioxide (CO₂),nitrogen (N₂), liquid natural gas (LNG), ammonia (NH₃), carbon monoxide(CO), argon (Ar), liquefied petroleum gas (LPG), hydrogen (H₂), hydrogensulfide (H₂S), air, C₁ to C₂₀ hydrocarbons, and combinations thereof;and a second component selected from the group consisting of organicacids, inorganic acids, peroxides, free radical producing chemicals,Lewis acids, humic depolymerization agents, olefin metathesis catalysts,reactive gases, enzymes, microbes, plasmas, catalysts, and combinationsthereof.
 13. The method of claim 1, wherein the step of transporting themobile kerogen-based product out of the subsurface shale formationcomprises using an extraction fluid.
 14. The method of claim 13, whereinthe extraction fluid is selected from the group consisting of carbondioxide (CO₂), nitrogen (N₂), liquid natural gas (LNG), ammonia (NH₃),carbon monoxide (CO), argon (Ar), liquefied petroleum gas (LPG),hydrogen (H₂), hydrogen sulfide (H₂S), air, C₁ to C₂₀ hydrocarbons, andcombinations thereof.
 15. The method of claim 13, wherein the extractionfluid is substantially indistinguishable from the reactive fluid. 16.The method of claim 1, wherein pumping is used to transport the mobilekerogen-based product out of the subsurface shale formation.
 17. Themethod of claim 1, wherein the extracted kerogen-based product isupgraded to yield one or more commercial petroleum-based products. 18.The method of claim 1, further comprising, after the step ofpressurizing and before the step of depressurizing, an interim step ofcontacting the shale with a heated fluid to enhance the thermal stressescreated in the subsurface shale formation.
 19. A method for extracting ahydrocarbon-based product from a low-permeability hydrocarbon-bearingsubsurface formation, the method comprising the steps of: a) increasingpermeability in a region of the subsurface formation to a fluid so as toestablish a region of enhanced permeability by (i) drilling a casedinjection well into the subsurface shale formation comprising thesubsurface shale; (ii) pressurizing the injection well with a densephase fluid to provide a pressurized well; (iii) contacting thesubsurface formation with a heated fluid to enhance thermal stressescreated in the subsurface formation; and (iv) rapidly de-pressurizingthe pressurized well to reach a steady state reduced pressure; b)contacting hydrocarbonaceous material in the region of enhancedpermeability with a reactive fluid to create a mobile hydrocarbon-basedproduct; and c) transporting the mobile hydrocarbon-based product out ofthe subsurface formation to yield an extracted hydrocarbon-basedproduct.
 20. The method of claim 19, wherein the sub-steps ofpressurizing and de-pressurizing are repeated.
 21. The method of claim19, wherein the dense phase fluid comprises a component selected fromthe group consisting of carbon dioxide (CO₂), nitrogen (N₂), liquidnatural gas (LNG), ammonia (NH₃), carbon monoxide (CO), argon (Ar),liquefied petroleum gas (LPG), hydrogen (H₂), hydrogen sulfide (H₂S),air, C₁ to C₂₀ hydrocarbons, and combinations thereof.
 22. The method ofclaim 19, wherein the step of contacting the hydrocarbons in thesubsurface formation with a reactive fluid to create a mobilehydrocarbon-based product involves a chemical modification of thehydrocarbon.
 23. The method of claim 19, wherein the reactive fluidcomprises a first component selected from the group consisting of carbondioxide (CO₂), nitrogen (N₂), liquid natural gas (LNG), ammonia (NH₃),carbon monoxide (CO), argon (Ar), liquefied petroleum gas (LPG),hydrogen (H₂), hydrogen sulfide (H₂S), air, C₁ to C₂₀ hydrocarbons, andcombinations thereof and a second component selected from the groupconsisting of organic acids, inorganic acids, peroxides, free radicalproducing chemicals, Lewis acids, humic depolymerization agents, olefinmetathesis catalysts, reactive gases, enzymes, microbes, plasmas,catalysts, and combinations thereof.
 24. The method of claim 19, whereinthe step of transporting the mobile hydrocarbon-based product out of thesubsurface formation comprises using an extraction fluid.
 25. The methodof claim 24, wherein the extraction fluid is selected from the groupconsisting of carbon dioxide (CO₂), nitrogen (N₂), liquid natural gas(LNG), ammonia (NH₃), carbon monoxide (CO), argon (Ar), liquefiedpetroleum gas (LPG), hydrogen (H₂), hydrogen sulfide (H₂S), air, C₁ toC₂₀ hydrocarbons, and combinations thereof.
 26. The method of claim 24,wherein the extraction fluid is substantially indistinguishable from thereactive fluid.
 27. A method for extracting a kerogen-based product froma subsurface shale formation comprising subsurface shale, wherein thesubsurface shale comprises an inorganic component in addition to thekerogen, the method comprising the steps of: a) increasing accessibilityof kerogen in subsurface shale to a fluid by (i) drilling a casedinjection well into the subsurface shale formation comprising thesubsurface shale; (ii) pressurizing the injection well with a densephase fluid to provide a pressurized well; (iii) contacting the shalewith a heated fluid to enhance the thermal stresses created in thesubsurface shale formation and (iv) rapidly de-pressurizing thepressurized well to reach a steady state reduced pressure, b) contactingthe kerogen in the subsurface shale with a reactive fluid to create amobile kerogen-based product; and c) transporting the mobilekerogen-based product out of the subsurface shale formation to yield anextracted kerogen-based product.